1. Field of the Invention
The present invention relates to a timing controller, and particularly, a timing controller and an Organic Light Emitting Diode (OLED) display device using the same, which reduce consumption power.
2. Discussion of the Related Art
Display devices such as LCD (Liquid Crystal Display), OLED (Organic Light Emitting Diode), PDP (Plasma Display Panel), and EPD (Electrophoretic Display) are manufactured through several steps. For manufacturing these display devices, an imprinting process using an imprinting apparatus is carried out so as to form a pattern on a substrate used for the display devices.
Flat Panel Display (FPD) devices, which decrease the weight and volume thereof corresponding to the limitations of Cathode Ray Tubes (CRTs), are being developed recently. As such FPD devices, there are Liquid Crystal Display (LCD) devices, Plasma Display Panels (PDPs), Field Emission Display (FED) devices, and electroluminescence devices.
Since PDPs are simple in structure and process, the PDPs are attracting much attention as display devices that are light, thin, short, and small, and have a large screen. However, the PDPs are low in emission efficiency, brightness, and consumption power.
Thin Film Transistor (TFT) LCD devices, using TFTs as switching elements, are FPD devices that are being widely used. However, since TFT LCD devices are non-emitting display devices, the TFT LCD devices have a narrow viewing angle and a slow response time.
On the contrary, electroluminescence devices are categorized into inorganic light emitting diode display devices and OLED display devices, based on materials of light emitting layers. Particularly, since OLED display devices use self-emitting elements that self emit light, the OLED display devices have a fast response time, high emission efficiency, high brightness, and a wide viewing angle.
FIG. 1 is a circuit diagram for describing the light emitting principle of a related art OLED display device. FIG. 2 is waveform diagrams for describing the cause of a flicker which arises in a related art LCD display device.
As a type of FPD device, an OLED display device that is as illustrated in FIG. 1 includes an OLED formed in each sub-pixel.
The OLED has an anode electrode and a cathode electrode, and includes an organic compound layer that is formed between the anode electrode and cathode electrode.
The organic compound layer includes a Hole Injection Layer (HIL), a Hole transport layer (HTL), an Emission Layer (EML), an Electron Transport Layer (ETL), and an Electron Injection Layer (EIL).
When a driving voltage is applied to the anode electrode and cathode electrode, a hole passing through the HTL and an electron passing through the ETL move to the EML to form an exciton, and thus the EML emits visible light.
In the OLED display device, a plurality of OLEDs including respective sub-pixels that are as illustrated in FIG. 1 are arranged in matrix type. The OLED display device supplies a scan pulse to selectively turn on thin film transistors PL and PT that are active elements, thereby selecting sub-pixels. Subsequently, the OLED display device controls the brightness of the selected sub-pixels with a supply voltage VDD, according to the grayscale levels of digital video data.
As another type of FPD device, LCD devices are thin and light and consume low power, and thus are being widely applied to computer monitors, notebook computers, portable terminals, and wall-mounted televisions.
The related art LCD device or OLED display device drives a panel at a fixed refresh rate (for example, 60 Hz or more), irrespective of the kinds of input images.
A timing controller, included in the related art LCD device or OLED display device, receives a video-related signal (hereinafter referred to as a video signal) from a graphic card (or called a system) and delivers the received signal to the panel as-is without changing a refresh rate (i.e., a frame driving frequency).
For example, when an LCD device or OLED display device with XGA-level resolution (for example, resolution of 1025×768 pixels) is driven at a frame driving frequency of 60 Hz, a vertical sync signal (Vsync) has a frequency of 60 Hz, a horizontal sync signal (Hsync) has a frequency of 48.4 KHz, and a pixel frequency is 65 MHz. Such frequencies are maintained as-is, regardless of various kinds of video signals.
As described above, since the related art LCD device or OLED display device always drives the panel at a fixed frame driving frequency (i.e., the refresh rate), constant consumption power by data transition occurs even when an input image is almost stationary as in documents.
In LCD devices or OLED display devices, as consumption power, there are static consumption power by a leakage current, and dynamic consumption power by transistors and capacitors.
Herein, data transition is associated with dynamic consumption power, which is divided into two kinds based on a transistor load and capacitor load. As a frame driving frequency becomes higher, consumption power increases.
For example, consumption power that is consumed by the sub-pixel of the OLED display device in FIG. 1 is expressed as Equation (1). Equation (1) shows that as an input frequency (i.e., a frame driving frequency) (fI) becomes higher, consumption power (PD) increases.PD=PT+PL=(Cpd×VCC2×fI)+(CL×VCC2×fO)   (5)where PD is a power-consumption capacitance, fI is an input frequency, CL is an external (load) capacitance, fO is an output signal frequency, and VCC is a supply voltage.
In the related art LCD device, when dynamically changing a frame driving frequency for decreasing consumption power, there is a high probability that an asymmetric component between an inter-frame positive data voltage and negative data voltage will is generated due to the polarity driving of the LCD device. Consequently, a flicker arises in the related art LCD device.
In the related art LCD device, when a positive data voltage VA in a portion (a) of FIG. 2 differs from a negative data voltage VB in a portion (b) of FIG. 2, a flicker arises. To provide an additional description, a data driver of the related art LCD device selectively uses positive data and negative data according to a polarity signal (POL), and when dynamically changing a refresh rate, there is much possibility that a flicker arises.
In the related art LCD device, even though not considering the above-described polarity driving, when a frame driving frequency decreases to less than a certain level (for example, to approximately 30 to 50 Hz), there is much possibility that a flicker arises, and thus, it is difficult to decrease the frame driving frequency to less than the certain level.
On the contrary, as described above, since the related art OLED display device has a fast response time by using self-emitting elements that self-emit light, there is small possibility that a flicker arises when a frame driving frequency decreases to a low level.
However, since the related art OLED display device displays an image at the same frame driving frequency even when receiving a fixed image where an input image is almost stationary as in documents, and particularly cannot differentiate a document and a moving image and differently change a frame driving frequency according to the document and moving image, the related art OLED display device unnecessarily consumes power when outputting a fixed image such as a document.